1. Field of the Invention
The invention pertains to the art of dual capacity hermetic refrigerant compressors for air conditioning and heat pump applications, and control arrangements therefor.
2. Discussion of Air Conditioning and Heat Pump Background
It has been determined from a study of heat pump economics for a heat pump operating in a heating mode that if the heat pump were capable of running efficiently at a lowered volumetric displacement on mild days while heating is occurring, and at a higher volumetric displacement on cold days, that this would provide definite economic advantages. One part of the problem with respect to heat pump capacities when operating in a heating mode is that the compressor capacity decreases at lower temperatures because of the lowered suction gas temperature and density so that the compressor is simply not fed a large enough quantity of refrigerant. Thus the compressor capacity is decreasing as the ambient temperature drops while the desirable condition would be that the capacity would be increasing as the temperature drops. Several ways of handling the problem is to provide multispeed compressors, or multiple and unloadable compressor cylinders or by oversizing the compressor to meet the heating needs, which will penalize the economics in northern situations with respect to the typical cooling needs and with respect to heating on milder days. It is my view that each of these arrangements for obtaining the capacity for heating has disadvantages as compared to an arrangement according to my invention.
3. Prior Patent Art Description
There are a significant number of prior patents teaching various means to change the output of a pump or other reciprocating member by changing the eccentricity of the orbiting means driving the connecting rod. Representative examples of such arrangements include U.S. Pat. Nos. 135,380; 2,592,237; 3,007,349; and 3,180,178, all of which provide the adjustment of the eccentricity is accomplished through means other than a simple reversal of rotation of the driving means for the device, such adjustments including manually rotating a gear or other arrangement as in the first three patents, and through a change in the hydraulic pressure of the lubricating system in the latter patent. I consider it unacceptable for a hermetic shell refrigerating compressor to be provided with any means external of the shell for providing the adjustment of eccentricity. The arrangement of the latter patent is also considered undesirable in that it calls for the hydraulic fluid actuated means to be mounted on the crankshaft and to rotate with it, as well as varying the lubrication pressure by either a manually operated pressure regulator or by an automatically operated pressure regulator controlled by the load on the air compressor which again would be undesirable with respect to a hermetic system.
It is not unknown in the patent art to provide arrangements in which variable stroke lengths are obtained through a reversal of direction of the driving means. U.S. Pat. No. 2,717,518 teaches a direction sensitive linkage lengthening arrangement particularly for use in depressed parking of vehicle windshield wipers. U.S. Pat. No. 3,482,458 teaches a dual stroke length mechanism particularly applicable to a reciprocating saw mechanism in which a pair of links associated with a rotating plate will give different stroke lengths depending upon the rotation of the plate. Neither of these arrangements would be suitable in a hermetic refrigeration compressor as a practical matter in my view, particularly because of the difference in magnitude of forces required in a compressor relative to that which linkages of the types disclosed could handle.